As a method for producing methionine, a method for producing methionine by hydrolyzing 2-amino-4-(methylthio)butanenitrile represented by formula (1) has been known for a long time. However, when a strong base is used as the hydrolysis condition, inorganic salts such as carbonates or sulfates are produced at the stage of neutralization after completion of the reaction, and thus a purification step so as to remove salts is required to obtain methionine. A condition without using a strong base has been studied as the hydrolysis condition of 2-amino-4-(methylthio)butanenitrile. However, in order to obtain methionine in good yield, the reaction should be performed under different reaction conditions since a condition for obtaining 2-amino-4-(methylthio)butanenitrile (methionine amide) represented by formula (2) from 2-amino-4-(methylthio)butanenitrile differs from a condition for obtaining methionine from methionine amide (see Patent Document 1). Therefore, this is not always a simple production method.
Although there has also been known a method for directly obtaining amino acid by reacting α-aminonitrile with water in the presence of zinc metal or zinc oxide (see Patent Document 2), the yield of methionine is not always satisfactory.
